The subject matter disclosed herein relates to X-ray tubes and, in particular, to attenuation features for secondary discharges of X-rays within an X-ray tube.
In non-invasive imaging systems, X-ray tubes are used in fluoroscopy, projection X-ray, tomosynthesis, and computer tomography (CT) systems as a source of X-ray radiation. Typically, the X-ray tube includes a cathode and a target. A thermionic filament within the cathode emits a stream of electrons towards the target in response to heat resulting from an applied electrical current, with the electrons eventually impacting the target. Once the target is bombarded with the stream of electrons, it produces focal and off-focal X-ray radiation.
The focal X-ray radiation traverses a subject of interest, such as a human patient, and a portion of the radiation impacts a detector or photographic plate where the image data is collected. Generally, tissues that differentially absorb or attenuate the flow of X-ray photons through the subject of interest produce contrast in a resulting image. In some X-ray systems, the photographic plate is then developed to produce an image which may be used by a radiologist or attending physician for diagnostic purposes. In digital X-ray systems, a digital detector produces signals representative of the received X-ray radiation that impacts discrete pixel regions of a detector surface. The signals may then be processed to generate an image that may be displayed for review. In CT systems, a detector array, including a series of detector elements, produces similar signals through various positions as a gantry is displaced around a patient.
Despite the electron stream colliding with the target in the proper location, some X-rays do not exit through the window, but instead are projected back through the X-ray tube, and may result in secondary radiation. This off-focal X-ray radiation generated in the X-ray tube must be contained within the unit so that the X-rays do not exit to the environment. Traditionally, X-ray attenuation has been provided through the use of lead linings placed along the outer periphery of the tube unit. Environmental awareness and regulation has made these techniques less desirable. Furthermore, full enclosure shielding can be bulky, requiring a large amount of shielding material. Accordingly, a need exists from improved off-focal X-ray shielding in X-ray tubes.